1. Field of the Invention
This invention relates to an elastomeric cap for closing the open end of a tubular member having at least one pipe of smaller diameter projecting through its open end. More particularly, the invention is concerned with such a cap for closing the open top of a vertical support member of a pipe support structure for a petroleum pipeline.
2. Description of the Prior Art
The Trans-Alaska Pipeline is being built and will extend from a location near Beechey Point on the North Slope of Alaska to Valdez near the south coast. It will pass through terrain where the ground is frozen the year-round, this ground being commonly referred to as the permafrost. The pipe itself is supported about 8 to 15 feet above the ground on support structures that are longitudinally spaced about 60 feet apart. Each support structure has two vertical support members that are transversely spaced with a horizontal beam extending between them. The pipe is carried by a saddle mounted on the horizontal beam.
Each vertical support member is a length of tubular steel casing having an outside diameter of eighteen inches, an inside diameter of 17 inches, and a length of up to 60 feet. The vertical support member is set into a cylindrical hole drilled in the permafrost with from about 10 to 20 feet of the casing extending above grade. The annulus between the casing and walls of the hole is filled with a grouting mixture of sand and water, which freezes and supports the casing in upright position.
It is important that the grouting mixture remains frozen. To assure that it does, a pair of heat pipes, each about 3 inches in diameter are inserted vertically into the casing. These heat pipes extend from near the bottom of the casing out through its top, and terminate a few feet above the top. The interior of the casing is packed with a moist sand to grade level, the moist sand surrounding the heat pipes. This moist sand then freezes to hold the heat pipes in place. These pipes contain refrigerant, and conduct heat from the frozen sand material inside the casing to the atmosphere above the top of the casing, where the heat is radiated or given off to the atmosphere. In this way, the frozen sand inside the casing and the frozen grout that surrounds the casing are prevented from thawing.
It is essential that the weather, particularly rain and snow, be excluded from the interior of the casing. Rain is especially detrimental, as it would tend to melt the sand inside and outside of the casing. It would also saturate the sand within the casing, and could later freeze and burst the casing.
Heretofore, steel caps have been used to close the top of the casing. However, these must be cut and fitted about the heat pipes and welded to the casing. Also, the joints between the metal parts must be filled with caulking compound. These operations are time-consuming and costly, and are often difficult or impossible to perform in the inclement arctic weather.